In current deployed transport networks, such as mobile transport networks, layer 2 transport switches may be used as aggregation sites to aggregate traffic from different cell sites and fixed access sites.
In packet backbone networks, site routers may be adopted at the edge of layer 2 networks (e.g., aggregation sites) to transmit layer 2 switch traffic to layer 3 Internet Protocol/Multiprotocol Label Switching (IP/MPLS) backbone networks (layer 3 networks). In other words, the site routers may act as a bridge from layer 2 to layer 3.
For example, as shown in FIG. 1, multiple layer 2 switches 104-116 may construct a site 102 (layer 2 network) having a ring topology closing with dual site routers 120, 122. Multiple routers 120, 122 may be used to provide static routing redundancy towards the layer 2 network 102 to protect against single point failures. The multiple routers 120, 122 may use Virtual Router Redundancy Protocol (VRRP). According to VRRP, one of the multiple routers 120, 122 may have a master/backup status as master and the remaining router or routers may have a master/backup status as backup. Upon failure of the router that has the master/backup status as master, a redundant router master/backup status change may occur and the backup router or one of the backup routers may then have a master/backup status as master.
Integrated Routing and Bridging (IRB) may combine router functionality with switch functionality in the dual site routers 120, 122. The Ethernet interfaces between the layer 2 transport switches (client nodes) and the Ethernet interfaces between the routers may be configured as layer 2 interfaces. IRB provides the ability to route between a bridged domain and a routed domain with Bridge Group Virtual Interface (BVI). BVI may be used on the routers 120, 122 towards the layer 2 switches.
In an aggregation site including switches and routers, Ethernet Ring Protection (ERP) may act as a ring protection mechanism to provide sub-50 ms protection and recovery switching for Ethernet traffic in a ring topology, and also ensure that no loops are formed at the Ethernet layer. A Ring Protection Link (RPL) Owner Node is responsible for blocking traffic at one end of the RPL to secure link switching during link failure or a recovery condition within the Ethernet ring so that traffic may move towards a layer 3 network 124.
In an aggregation site, such as the aggregation site 102 shown in FIG. 1, ERP is normally supported by the switches 104-116. In order to provide resilience within the whole ring, ERP may be used if all the switches 104-116 support the ERP feature. Alternatively, some switches may not support the ERP feature and may run Spanning-Tree Protocol (STP). In such an instance, an ERP-capable switch can send a Topology Change Notification Bridge Protocol Data Unit (TCN BPDU) to non-ERP switches triggering a MAC Forwarding Database (FDB) flush.
In an aggregation site, such as the aggregation site 102 shown in FIG. 1, once a link or switch failure occurs, the layer 2 network ring will switch based on a configured resilience mechanism such as ERP switching. The failed link or switch will be blocked and traffic will instead go through the unblocked protection link towards the layer 3 network 124 through the site routers 120, 122. For example, as shown in FIG. 1, no switch or link failure has occurred. The layer 2 network ring is such that, for example, traffic from switch 106 is directed through switches 108, 110, 112. FIG. 2 shows the same aggregation site 102 as in FIG. 1 after a link failure. Specifically, the link between switches 110 and 112 is shown as failed. Thereafter, the layer 2 network ring changes and traffic from switch 106 is redirected through switches 104, 116, 114.
However, there remains a need for improvement with respect to switch or link failure handling.